Many developmental processes in invertebrate and vertebrate organisms depend on the specific interactions between different cells and cells and components of the extracellular matrix. How highly organized and sophisticated structures, such as the nervous system, are put together by genetic and interactive programs is still largely unknown. Using the fruitfly Drosophila melanogaster as the experimental system, the significance and role of the homophilic cell adhesion molecule (CAM) neuroglian for the development of neuronal and other cells will be studied. The nature of signals that adhesion molecules, such as Drosophila neuroglian, might transmit across the plasma membrane of their host cell is the focus of the present proposal. The research proposed here seeks to establish experimental evidence for the functional regulation of the Drosophila neuroglian molecule by cytoplasmic interactions and protein modifications and its potential involvement in a signal transduction across the cell membrane. First the type and status of the phosphate groups that are covalently attached to the neuroglian molecule will be determined. Functionally relevant changes in the phosphorylation status of the neuroglian protein or a second messenger response caused by the homophilic neuroglian binding reaction will then be investigated. In vitro mutagenesis will be used to probe the domains or specific amino acid residues of the neuroglian polypeptide that are suspected to be involved in signal transduction or neuroglian regulation. In particular the requirement for the cytoplasmic neuroglian domain in the homophilic binding process will be tested. "Mutagenized" cDNAs will be introduced into the Drosophila S2 cell lines by transfection or into neuroglian deficient Drosophila embryos by transposase-mediated gene transfer to investigate their properties and possible phenotypes. Suspected functional interactions between neuroglian and other gene product(s) (e.g. protein kinases, protein phosphatases of G-proteins) will be tested using the Drosophila S2 cell transfection assay as well as genetic level. The proposed experiments will contribute to our understanding of how CAMs in general are involved in developmental and other biological processes.